Shipping charges are not always determined by weight. A large, heavy box may be more expensive due to the space it requires in a truck or plane. That's where dimensional weight plays a role. Carriers determine the weight based on package size and dimensions to generate an estimate that they compare with the actual weight of the package to arrive at the billable weight.
Cubic pricing also applies to small, dense packages, especially those sent by USPS. Cubed rates are based on the volume of eligible small parcels and the applicable cubic tier, rather than dimensional weight. Learning about both can help you better estimate shipping costs, select packaging to suit your needs, and prevent unexpected expenses. You'll find formulas, calculation steps, and examples for dimensional weight and cubic rates below.
What is Dimensional Weight?
The term dimensional weight, often referred to as DIM weight or volumetric weight, is a shipping term that turns a package's volume into a weight equivalent. When there is a lot of space but not much weight, carriers use it. The basic formula is length x width x height divided by the DIM divisor.
The DIM weight is then compared with the actual weight of the package. If the dimensional weight is larger, it may be used as the billable weight to determine the shipping charge. Both UPS and FedEx use dimensional weight calculations, but the divisor may differ depending on the carrier, service, dimensional weight calculation type, and shipment.
How to Calculate Dimensional Weight?
Dimensional weight is calculated by multiplying the length and width by the height and then dividing by the carrier's DIM divisor. Round to the carrier's specification, and then compare to the actual weight. The highest applicable weight is typically the billable weight.
Step 1: Measure the Package Dimensions
Find the length, width, and height of the fully packed box. Utilize the extreme points of the package, such as bulges or irregular places that enlarge the package. You can also build carrier measurement rules that will round the dimensions prior to the calculation. For instance, UPS tells shippers to take the longest dimensions and round up to the nearest whole number.
Step 2: Calculate the Cubic Size
Calculate the volume of all the packages by multiplying the three dimensions of each package:
Length × Width × Height = Cubic Size
For instance, the cube of 20 x 15 x 10 is:
20 × 15 × 10 = 3,000 cubic inches
This gives you an idea of the volume it takes up in space.
Step 3: Divide by the DIM Divisor
Calculate the cubic size, then divide by the appropriate carrier divisor:
Dimensional Weight = Cubic Size / DIM Divisor
For instance, if the divisor is 139:
3,000 ÷ 139 = 21.58 lb
After rounding up, the dimensional weight is 22 lb.
A divisor is not universal. For instance, UPS is currently pricing 139 for Daily Rates and 166 for Retail Rates on its U.S. shipping guidance, and FedEx's published calculation is based on 139 for U.S. international shipments. Before you make a final charge calculation, always verify the carrier or service you are using.
Step 4: Compare DIM Weight With Actual Weight
Then, compare the calculated dimensional weight against the actual weight of the package. For example:
Actual weight: 18 lb
DIM weight: 22 lb
Billable weight: 22 lb
If the actual weight were equal to 25 lb, the actual weight would be greater, and the applicable billable weight would likely be 25 lb. The specific billing rule may differ depending on the carrier or service and should be referenced through the relevant Rate Guide for the shipment.
What are Cubic Rates?
Cubic rates are the rates charged for shipping based on the physical size of a parcel and not dimensional weight or actual weight. They are priced based on a qualifying shipment's cubic dimension and rate tier for certain small, dense packages.
USPS sets cubic rates for eligible commercial Priority Mail items. As of now, qualifying cubic mailpieces must normally be no more than 20 pounds or 0.50 cubic foot in length and no longer than 22 inches. Cubic pricing is based on volume tiers, and the applicable postage is also determined by the shipping zone and service.
How to Calculate Cubic Rates?
To find the cubic volume of any package, multiply length x width x height, then divide by 1,728 to get cubic feet. If the package qualifies for the carrier's cubic eligibility, enter the result in the applicable cubic tier and rate for the package's service and zone.
Step 1: Measure Length, Width, and Height
Take outside measurements of the completed package. Apply the measurement and rounding rules provided by the carrier when determining the volume. If a parcel has the following dimensions:
12 × 10 × 6 inches
Step 2: Calculate Cubic Inches
Calculate the volume by multiplying the three dimensions:
12 × 10 × 6 = 720 cubic inches
This is the package's volume.
Step 3: Convert Cubic Inches to Cubic Feet
To convert the cubic inches to cubic feet, divide by 1,728.
720 ÷ 1,728 = 0.417 cubic feet
The volume of the package is thus about 0.42 cubic feet.
Step 4: Find the Cubic Tier
If the cubic volume is known, determine the applicable tier. Common cube roots are:
0.10 cubic feet or less
- More than 0.10 up to 0.20 cubic feet
- More than 0.20 up to 0.30 cubic feet
- More than 0.30 up to 0.40 cubic feet
- More than 0.40 up to 0.50 cubic feet
In the above example, 0.417 cubic feet would be classified in the 0.50 cubic-foot category. USPS charges by cubic foot range and zone, so the actual postage varies based on USPS service and destination zone.
Step 5: Check Cubic Eligibility and Rate
There are cubic rates that are not calculated by volume. Determine if the package qualifies for the carrier's program based on a maximum volume, weight, dimensions, and service restrictions.
The package is subject to current USPS commercial cubic pricing, which typically applies when the package is 0.50 cubic foot or less, weighs 20 pounds or less, and is 22 inches or less in length of the longest dimension. After you qualify, select from the appropriate cubic tier and zone to determine the shipping rate.
Dimensional Weight vs. Cubic Rates
Both dimensional weight and cubic rates base packages on volume, but they are calculated differently. Dimensional weight is the measurement of a package's volume in a theoretical weight, which varies by carrier. This weight is then compared to the actual weight to calculate the billable weight.
Cubic pricing is a pricing model based on the volume of the package. It's typically used to send out small amounts of mail, not large packages with low density. Cubic pricing is a volume based pricing structure, and DIM (Dimensional Weight) is a weight-based calculation based on size.
Conclusion
The formula used to calculate dimensional weight is length x width x height / DIM divisor. You then compare the result to the actual weight to decide on the billable weight. Cubic rates, however, will be calculated differently. Determine the service and zone for which the shipment is being sent, verify the carrier's eligibility criteria, select the appropriate cubic tier, and then apply the applicable rate to the shipment.
As the divisor, eligibility rules and shipping prices may differ from one carrier to another and from one service to another, so please always refer to the current carrier guidelines for the final shipping quote.
FAQs
What is the formula for dimensional weight?
The basic formula is Length x Width x Height / DIM divisor = dimensional weight. The applicable divisor may change based on carrier, service, rate type, and measurement system. Please review the carrier's current rules before calculating billable weight.
How do you calculate cubic feet for shipping?
Find the length x width x height of the package in inches to get the number of cubic inches. Now divide that number by 1,728 to convert it to cubic feet.
Is dimensional weight equal to cubic pricing?
No. Dimensional weight is a weight calculation based on package volume. Cubic pricing is based on the volume of the package to determine a shipment's eligibility for a specific pricing tier.
What is the difference between actual weight and dimensional weight?
Actual weight is the weight of the package as it is measured on a scale. Dimensional weight is based on the package size, and if required by the applicable carrier rules, it will be based on the higher of actual or dimensional weight.
What types of packages are eligible for USPS cubic pricing?
Currently, the USPS commercial cube eligibility is approximately 0.50 cubic feet or less, 20 pounds or less, and no more than 22 inches in length. There may be other service specific needs, so consult current USPS regulations before mailing.
